1. Technical Field
The present invention relates to a pretreatment liquid, an oil-based ink jet printing ink set, and an oil-based ink jet printing method.
2. Related Art
Development of office use ink jet printers is underway. Office use printers are required to provide high-quality, high-speed printing on plain paper and other print media and to have a function as a finisher that can, for example, bind printed sheets. Accordingly, the inks used in such printers are required to allow the printer to print high-density images on plain paper at a high speed, and also required to reduce strike-through in view of duplex printing. Furthermore, such inks are required not to cause cockling, curling, or any other deformation of paper after high-speed printing. Aqueous inks containing aqueous solvent can cause deformation of plain paper, such as cockling or curling, when used for high-speed printing. Accordingly, oil-based inks containing an organic solvent, unlikely to cause paper deformation are being developed.
If a volatile organic compound is used as the medium of an oil-based ink, the volatile organic compound can cause health damage such as allergies when being released to environment. Therefore, low-volatile organic compounds are used as the media of oil-based inks. However, if an oil-based ink containing a low-volatile organic compound as the medium is used for printing, the medium is likely to remain in the paper due to the low volatility thereof. The remaining medium can penetrate the paper and thus cause strike-through and bleeding or reduce the print density from the initial print density. If a graphic or a document printed on a print medium with an oil-based ink is put in a polypropylene (PP) clear folder, the organic solvent in the ink can migrate to the clear folder, thereby swelling the inner surfaces of the folder and thus deforming the clear folder in such a manner that both sides thereof warp outwards or waved. In particular, when printed matter created at a high duty is put in a clear folder, the clear folder is warped outwards and the use thereof is hindered.
In an approach to a solution of these disadvantages (for example, JP-A-2009-275211), clear folder deformation is reduced by increasing the viscosity of the ink to suppress the migration of the organic solvent from the print medium to the clear folder, and using a high polar medium to relieve the effect of attacking the clear folder. In this case, the medium is a diester of a polyhydric alcohol and a branched-chain aliphatic carboxylic acid or a diester of a branched-chain aliphatic alcohol and a high aliphatic carboxylic acid.
Unfortunately, if the viscosity of the ink or the polarity of the medium is excessively high, a problem occurs in ejecting ink, or the suppression effect of clear folder deformation is insufficient and lasts only for a short time of not more than about 10 days. Further, printed sheets are likely to stick to each other when a stack thereof has been stored. It is thus difficult to suppress the deformation of the clear folder caused by printed matter created using an oil-based ink for a long time.